Proximal ear hole injury heals by limited regeneration during the early postnatal phase in mice.

Ear pinna is a particular feature of mammals that shows several repair responses depending on age. Two millimeter hole made in the pinna of middle-aged female mice heals due to partial reconstitution of new tissues (limited regeneration), whereas a hole punched in the ear of young mice forms a scar tissue. In these studies, the injury is made in the center of the ear pinna, but little is known about the type of reparative response along the proximodistal polarity of the ear. This study evaluated the effect of pinna polarity, age, and sex in the ear hole-repairing response in Balb/c mice. Proximal injuries were repaired more efficiently by limited regeneration than wounds made in the middle region. Non-injured ear histological analysis revealed a higher presence of muscle, adipose tissue, cartilage, and larger blood vessels in the proximal ear area, which could influence ear hole closure by limited regeneration. To evaluate the healing response during ear growth, we punched a standard hole in the proximal area of the ear on postnatal day 21 and 8-month-old mice (adults). Thirty-five days after the wound, both groups reached the same wound closure, despite the greater proportional size of holes made in the younger mice. Ear growth also improved ear hole closure in male mice. These results suggest that ear growth accelerates hole closure, providing an example of enhanced regenerative abilities in growing structures. Finally, hole closure kinetics in the growing ear indicated an early re-differentiation phase exhibited at 14 days post-wound. In conclusion, ear topography and growth positively influenced the healing response to ear holes, making it a tractable model to study in mammals.

miR-31, miR-155, and miR-221 Expression Profiles and Their Association With Graft Skin Tolerance in a Syngeneic vs Allogeneic Murine Skin Transplantation Model.

Grafting is the preferred treatment for severe skin burns. Frequently, allogeneic tissue is the only transient option for wound coverage, but their use risks damage to surrounding tissues. MicroRNAs have been associated with acute rejection of different tissues/organs. In this study, we analyzed the expression of miR-31, miR-155, and miR-221 and associate it with graft tolerance or rejection using a murine full-thickness skin transplantation model. Recipient animals for the syngeneic and allogeneic groups were BALB/c and C57BL/6 mice, respectively; donor tissues were obtained from BALB/c mice. After 7 days posttransplantation (DPT), the recipient skin and grafts in the syngeneic group maintained most of their structural characteristics and transforming growth factor (TGF)-ß1 and TGF-ß3 expression. Allografts were rejected early (Banff grades II and IV at 3 and 7 DPT, respectively), showing damage to the skin architecture and alteration of TGF-ß3 distribution. miRNAs skin expression changed in both mouse strains; miR-31 expression increased in the recipient skin of syngeneic grafts relative to that of allogeneic grafts at 3 and 7 DPT (P < .05 and P < .01, respectively); miR-221 expression increased in the same grafts at 7 DPT (P < .05). The only significant difference between donor tissues was observed for miR-155 expression at 7 DPT which was associated with necrotic tissue. Only miR-31 and miR-221 levels were increased in the blood of BALB/c mice that received syngeneic grafts after 7 DPT. Our data suggest that local and systemic miR-31 and miR-221 overexpression are associated with graft tolerance.

The complexity of TGFß/activin signaling in regeneration.

The role of transforming growth factor ß TGFß/activin signaling in wound repair and regeneration is highly conserved in the animal kingdom. Various studies have shown that TGF-ß/activin signaling can either promote or inhibit different aspects of the regeneration process (i.e., proliferation, differentiation, and re-epithelialization). It has been demonstrated in several biological systems that some of the different cellular responses promoted by TGFß/activin signaling depend on the activation of Smad-dependent or Smad-independent signal transduction pathways. In the context of regeneration and wound healing, it has been shown that the type of R-Smad stimulated determines the different effects that can be obtained. However, neither the possible roles of Smad-independent pathways nor the interaction of the TGFß/activin pathway with other complex signaling networks involved in the regenerative process has been studied extensively. Here, we review the important aspects concerning the TGFß/activin signaling pathway in the regeneration process. We discuss data regarding the role of TGF-ß/activin in the most common animal regenerative models to demonstrate how this signaling promotes or inhibits regeneration, depending on the cellular context.

Mechanisms of epithelial thickening due to IL-1 signalling blockade and TNF-α administration differ during wound repair and regeneration.

IL-1 and TNF-α are always present during wound repair, but their pleiotropic and synergistic effects are incompletely understood. In this work, we evaluated the role of IL-1 in wound repair, and examined whether TNF-α administration impaired scarless wound repair. First, we characterised wound repair in outbred CD-1 mice according to age and sex in an ear punch wound model. Then, we examined the effects of Interleukin 1 receptor antagonist (IL-1ra) and TNF-α placement inside ear wounds by means of loaded Heparin beads in young and middle-aged male and female mice. Wounds in middle-aged females repaired with scarless characteristics, whereas those in young males showed fibrotic scarring. Rather than improving wound repair in young males, IL-1 signalling blockade increased epithelial thickness and IL-1ß and TNF-α expression, and diminished epidermal apoptosis. TNF-α impaired wound repair in middle-aged females, which exhibited acanthosis and overexpression of IL-1, but no change in apoptosis. These findings suggest that this mechanism of epidermal thickening differs from that observed in IL1-ra-treated animals.

A novel hydrogel of poloxamer 407 and chitosan obtained by gamma irradiation exhibits physicochemical properties for wound management.

Application of polymers cross-linked by gamma irradiation on cutaneous wounds has resulted in the improvement of healing. Chitosan (CH) and poloxamer 407 (P407)-based hydrogels confer different advantages in wound management. To combine the properties of both compounds, a gamma-irradiated mixture of 0.75/25% (w/w) CH and P407, respectively, was obtained (CH-P), and several physical, chemical, and biological analyses were performed. Notably, gamma radiation induced changes in the mixture's thermal behavior, viscosity, and swelling, and exhibited stability at neutral pH. The thermal reversibility provided by P407 and the bacteriostatic effect of CH were maintained. Mice full-thickness wounds treated with CH-P diminished the wound area during the first days. Consequently, with this treatment, increased levels of macrophages, α-SMA, and collagen deposition in wounds were observed, indicating a more mature scar tissue. In conclusion, the new hydrogel CH-P, at physiologic pH, combined the beneficial characteristics of both polymers and produced new properties for wound management.

Molecular control of cell differentiation and programmed cell death during digit development.

During the hand plate development, the processes of cell differentiation and control of cell death are relevant to ensure a correct shape of the limb. The progenitor cell pool that later will differentiate into cartilage to form the digits arises from undifferentiated mesenchymal cells beneath the apical ectodermal ridge (AER). Once these cells abandon the area of influence of signals from AER and ectoderm, some cells are committed to chondrocyte lineage forming the digital rays. However, if the cells are not committed to chondrocyte lineage, they will form the prospective interdigits that in species with free digits will subsequently die. In this work, we provide the overview of the molecular interactions between different signaling pathways responsible for the formation of digit and interdigit regions. In addition, we briefly describe some experiments concerning the most important signals responsible for promoting cell death. Finally, on the basis that the interdigital tissue has chondrogenic potential, we discuss the hypothesis that apoptotic-promoting signals might also act as antichondrogenic factors and chondrogenic factors might operate as anti-apoptotic factors.